Re: [PATCH v2] i2c/designware: enable i2c controller to suspend/resume asynchronously

[Andy Shevchenko <andriy.shevchenko@linux.intel.com>]

On Mon, 2016-02-01 at 17:04 +0200, Jarkko Nikula wrote:
> On 01/15/2016 08:38 AM, Fu, Zhonghui wrote:
> > Now, PM core supports asynchronous suspend/resume mode for devices
> > during system suspend/resume, and the power state transition of one
> > device may be completed in separate kernel thread. PM core ensures
> > all power state transition dependency between devices. This patch
> > enables designware i2c controllers to suspend/resume
> > asynchronously.
> > This will take advantage of multicore and improve system
> > suspend/resume
> > speed. After enabling all i2c devices, i2c adapters and i2c
> > controllers
> > on ASUS T100TA tablet, the system suspend-to-idle time is reduced
> > to
> > about 510ms from 750ms, and the system resume time is reduced to
> > about
> > 790ms from 900ms.
> > 
> > Signed-off-by: Zhonghui Fu <zhonghui.fu@linux.intel.com>
> > ---
> > Changes in v2:
> > - Move the device_enable_async_suspend() call into i2c_dw_proble()
> > 
> >   drivers/i2c/busses/i2c-designware-core.c |    1 +
> >   1 files changed, 1 insertions(+), 0 deletions(-)
> > 
> > diff --git a/drivers/i2c/busses/i2c-designware-core.c
> > b/drivers/i2c/busses/i2c-designware-core.c
> > index ba9732c..5d6ad27 100644
> > --- a/drivers/i2c/busses/i2c-designware-core.c
> > +++ b/drivers/i2c/busses/i2c-designware-core.c
> > @@ -861,6 +861,7 @@ int i2c_dw_probe(struct dw_i2c_dev *dev)
> > 
> >   	init_completion(&dev->cmd_complete);
> >   	mutex_init(&dev->lock);
> > +	device_enable_async_suspend(dev->dev);
> > 
> I'm aware Andy had concerns about about stability and you also
> mention 
> in another thread:
> 
> "if enable all LPSS devices suspend/resume asynchronously, the
> system 
> can't resume sometimes on ASUS T100TA(BayTrail-T SoC). But, I have 
> verified that the system can resume normally every time if enable
> only 
> i2c controller async mode and let other LPSS devices in sync mode on 
> ASUS T100TA.".
> 
> What I'm thinking would this change move things forward and help to
> find 
> out what potential underlying issues there are in LPSS code.
> 
> I'm fine with this I2C side change but can we assure we don't 
> accidentally enable the same on other LPSS devices before finding
> the 
> root cause for the crash?

Besides that we have to be really aware about DMA power related fix
introduced in v4.5-rc1 in acpi_lpss.c [1]. So, I would like to see a
wide testing especially on Intel Baytrail / Braswell platforms before
enabling it.

[1] http://comments.gmane.org/gmane.linux.acpi.devel/80263

-- 
Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Intel Finland Oy